Current supply control apparatus for inductance load

ABSTRACT

The present invention relates to a current supply control apparatus capable of actuating a large inductance load at a low electric power source voltage and also capable of improving a responsibility in a current supply control of the inductance load. When a detecting voltage of an absolute value circuit (10) representing a current value flowing in an exiting coil (1), provided as an inductance load, exceeds a standard voltage, transistors (3a, 3b) interposed between a DC electric power source (2a, 2b) and the exciting coil are turned off, and a magnetic energy stored in the exciting coil is utilized to charge a capacitor (5) up to a high voltage so that a current flowing after the transistors have been turned off is quickly reduced. Furthermore, when the detecting voltage decreases down to a predetermined value, the transistors are turned on, and then both a voltage charged in the capacitor and a voltage of the DC electric power source are applied to the exciting coil to cause the exciting current to be sharply increased. With this arrangement, the exciting current can be made to respond sharply to the standard voltage without specially applying a high voltage from the DC electric power source to the inductance load.

TECHNICAL FIELD

The present invention relates to a current supply control apparatus foran inductance load such as a magnetic bearing, a reluctance type motor,a stepping motor etc., more particularly to a current supply controlapparatus capable of actuating a large inductance load without using ahigh voltage electrical power source, thereby improving a responsibilityin a current supply control for an inductance load.

BACKGROUND ART

Conventionally, in the case where a large inductance load has to beactuated, a current supply control circuit is interposed between theinductance load and a high-voltage electrical power source so that anapplication of high voltage can be controlled by the current supplycontrol circuit. For example, in order to realize a magnetic levitationof a rotor member in a magnetic bearing (i.e. a linear motor) using anelectromagnet associated with a large inductance exciting coil, a highvoltage is applied to the exciting coil so as to steeply build up anexciting current.

Furthermore, in a reluctance type motor with an exciting coil having afairly large inductance for its armature, a voltage 5˜10 times as largeas a normal voltage for obtaining a normal motor output torque isapplied to a current supply circuit during a building-up period of anexciting current in order to promptly build up the exciting current forpreventing the motor output torque from being undesirably reduced. Also,a magnetic energy stored in the exciting coil is returned to an electricpower source during a trailing-edge period of the exciting current,thereby quickly decreasing the exciting current to prevent a countertorque from being generated.

However, a voltage required for realizing a magnetic levitation of arotor member in a magnetic bearing or a voltage applied to an excitingcoil of a reluctance motor for building up an exciting coil are so largethat a voltage of the electric power source becomes excessively large.

Furthermore, if an applied voltage to a reluctance motor is notsufficient, a building-up and a trailing-edge of an exciting currentbecome so dull that not only a torque reduction appears in itsbuilding-up period but a counter-torque occurs in its trailing-edgeperiod. This means that the motor cannot be driven at a high speed.

For example, in the case where a conventional reluctance type motor isdriven by a battery as a driving source of an automotive vehicle, therotational speed of the motor cannot be increased more than severalhundreds rpm. Thus, the motor will not have any practical use. Astepping motor also has similar problems.

SUMMARY OF INVENTION

The purpose of the present invention is to provide a current supplycontrol apparatus capable of actuating a large inductance load withoutusing a high-voltage electric power source and also capable of improvinga responsibility in a current supply control for an inductance load.

In order accomplish above purposes, the present invention provides acurrent supply control apparatus for an inductance load comprising: afirst and a second switching elements interposed between a DC electricpower source and said inductance load; a first and a second diodesinversely connected to respective connecting units each consisting ofcorresponding one of said first and second switching elements and aninductance load; a current detecting circuit for generating a detectingvoltage representing a current flowing in said inductance load; aback-flow preventing diode connected in a forward direction with respectto the DC electric power source on the DC electric power source side; acapacitor connected to said back-flow preventing diode; and a choppercircuit for comparing said detecting voltage of the current detectingcircuit with a standard voltage being variably set in a voltage waveformso as to turn on or off said first and second switching elementsdepending on the result of comparison.

Whereby, when the detecting voltage exceeds the standard voltage, thefirst and second switching elements are turned off; during thisturning-off period of the switching element, a magnetic energy stored inthe inductance load is prevented from being returned to the DC electricpower source by said back-flow preventing diode; the magnetic energy issupplied through said first and second diodes to the capacitor to chargeit up with a high voltage, thereby causing a current flowing in theinductance load after the switching element has been turned off isquickly reduced; and

when the detecting voltage decreases down to a predetermined value, thefirst and second switching elements are turned on to cause a highvoltage equal to a sum of the voltage charged in the capacitor and avoltage of the DC electric power source to be applied to the inductanceload so that a current flowing in the inductance load can be built upsharply.

Preferably, the current supply control apparatus further comprises acharging inductance, a third switching element interposed between saidback-flow preventing diode and said charging inductance, and a thirddiode interposed between said charging inductance and the capacitor,wherein a magnetic energy stored in the charging inductance is suppliedto the capacitor through the third diode, when the third switchingelement is turned off.

As described above, in accordance with the present invention, when thedetecting voltage representing the current flowing in the inductanceload exceeds the standard voltage, the first and second switchingelements interposed between the DC electric power source and theinductance load are turned off. Simultaneously, the capacitor is chargedup with a high voltage by virtue of the magnetic energy stored in theinductance load. Thus, the current flowing in the inductance load afterthe switching element has been turned off is quickly reduced.

When the detecting voltage has decreased down to the predeterminedvalue, the first and second switching elements are turned on. Thus, thehigh voltage equal to the sum of the voltage charged in the capacitorand the voltage of the DC electric power source is applied to theinductance load, causing the current flowing in the inductance load tobe increased sharply.

Accordingly, storage and discharge of the magnetic energy can bepromptly carried out without applying a higher voltage from the DCelectric power source to the inductance load for quick rise and fall ofexciting current. That is, responsibility of the exciting current withrespect to the standard voltage can be improved.

Preferably, when the third switching element interposed between theback-flow preventing diode and a charging inductance is turned off, themagnetic energy stored in the charging inductance is supplied to thecapacitor through the third diode. As a result, the responsibility ofthe exciting current control can be further improved.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a circuit diagram showing a current supply control apparatusin accordance with a first embodiment of the present invention appliedto a magnetic bearing;

FIG. 2 is a graph showing a standard voltage applied to the apparatus ofFIG. 1 and an exciting current flowing in an exciting coil of themagnetic bearing, together with an enlarged view of the exciting currentversus time;

FIG. 3 is a circuit diagram showing a current supply control apparatusin accordance with a modified description of the preferred embodiment;

FIG. 4 is a circuit diagram showing a current supply control apparatusin accordance with a second embodiment of the present invention appliedto a two-phase reluctance type motor;

FIG. 5 is a graph showing position detecting signals applied to theapparatus of the second embodiment and the exciting current flowingthrough the exciting coil of the motor, together with position detectingsignals applied to the apparatus of the modified example of the secondembodiment;

FIG. 6 is a circuit diagram showing a current supply control apparatusin accordance with a third embodiment of the present invention appliedto a motor;

FIG. 7 is a circuit diagram showing a current supply control apparatusin accordance with a modified example of the third embodiment;

FIG. 8 is a circuit diagram showing a current supply control apparatusin accordance with a fourth embodiment of the present invention appliedto a three-phase full-wave reluctance type motor;

FIG. 9 is a graph showing position detecting signals applied to theapparatus of FIG. 8 and an exciting current of the motor, together withan exciting current of the conventional motor;

FIG. 10 is a circuit diagram showing a current supply control apparatusin accordance with a modified example of the fourth embodiment;

FIG. 11 is a circuit diagram showing a current supply control apparatusin accordance with a fifth embodiment of the present invention appliedto a six-phase half-wave stepping motor; and

FIG. 12 is a graph showing pulse signals applied to the apparatus ofFIG. 11 and an exciting current of the motor.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, a current supply control apparatus in accordance with afirst embodiment of the present invention will be explained.

This current supply control apparatus serves to control an excitingcurrent supplied to an exciting coil for a magnetic bearing as aninductance load. As shown in FIG. 1, the current supply controlapparatus comprises a transistor 3a interposed between a positive outputterminal 2a of a DC electric power source and one end of an excitingcoil 1, and a transistor 3b interposed between a negative outputterminal 2b of the DC electric power source and the other end of theexciting coil 1. A magnetic core of the exciting coil 1 is omitted inFIG. 1. A diode 4a is inversely connected to a serial connecting unitconsisting of the transistor 3a and the exciting coil 1. A diode 4b isinversely connected to a serially connected unit consisting of thetransistor 3b and the exciting coil 1.

A back-flow preventing diode 6 is interposed between the positive outputterminal 2a of the DC electric power source and the transistor 3a so asto be connected in a forward direction with respect to the DC electricpower source, whereas a capacitor 5 having a small capacitance isconnected in parallel with the diode 6.

Furthermore, a resistance 0 for detecting a current flowing through theexciting coil 1 is interposed between the transistor 3b and the negativeoutput terminal 2b of the DC electric power source, whereas an absolutevalue circuit 10 consisting of a rectification circuit 10 is connectedbetween both ends of the resistance 9 for detecting a voltage drop inthe resistance 9 provided for indicating the resistance 9.

An output terminal of the absolute value circuit 10 is connected to anegative input terminal of an operational amplifier 11, whereas apositive input terminal of the operational amplifier 11 is connected toa standard voltage input terminal 12. An output terminal of theoperational amplifier 11 is connected to an input terminal of anamplification circuit 7. Further, an output terminal of theamplification circuit 7 is not only connected to a base of thetransistor 3b but also connected to a base of the transistor 3a throughan inversion circuit.

In the current supply control circuit constituted as above, a standardvoltage 14 shown in FIG. 2 is applied to the standard voltage inputterminal 12 of the current supply control circuit. In accordance with anapplication of the standard voltage 14, an H-level output sent out fromthe operational amplifier 11 is amplified in the amplification circuit 7and, in turn, supplied to the transistor 3a through the inversioncircuit and directly the transistor 3b, thereby effecting the continuitybetween both transistors 3a and 3b.

As a result, the DC electric power source voltage is supplied to theexciting coil 1 through the diode 6, both transistors 3a and 3b and theresistance 9. When the exciting coil is supplied with current, theexciting current builds up as shown by a broken line 15 in FIG. 2.

Subsequently, if the exciting current increases until an output of theabsolute value circuit 10 exceeds the standard voltage 14 applied to thepositive input terminal of the operational amplifier 11, an output ofthe operational amplifier 11 changes from an H-level to an L-level toturn off the transistors 3a and 3b.

In this instance, the back-flow preventing diode 6 prevents a largemagnetic energy stored in the exciting coil 1 from returning to the DCelectric power source through the diodes 4a and 4b. On the other hand,the stored magnetic energy flows into the capacitor 5 to charge it up toa high voltage with polarities shown in the drawing. That is, themagnetic energy of the exciting coil 1 is converted to the electrostaticenergy of the capacitor 5. Thus, the exciting current decreases steeply.

When the exciting current decreases down to a predetermined valuedefined from a hysteresis characteristics of the operational amplifier11, the output of the operational amplifier 11 returns to an H-level toturn on the transistors 3a and 3b. In this instance, a higher voltageequal to the sum of a charged voltage of the capacitor and a voltage ofthe DC electric power source is applied to the exciting coil 1 tosharply build up the exciting current.

Subsequently, the exciting current will be further increased by the DCelectric power source voltage. When the exciting current increases up toa value corresponding to the standard voltage 14, the output of theoperational amplifier changes to an L-level to turn off the transistors3a and 3b. In this manner, the exciting current is chopper-controlled bya chopper circuit consisting of the amplifier circuit 7, the resistance9, the absolute value circuit 10, and the operational amplifier 11,whereby the exciting current is caused to change along a curve 15 whichis proportional to the standard voltage 14.

Next, the chopper control is further explained with reference to FIG. 2showing an enlarged view of the exciting current versus time in avicinity of time point at which the circuit is energized, which isdenoted by a broken line 16.

When the transistors 3a and 3b are turned on, a high-voltage due to anelectrostatic energy stored in the capacitor 5 is applied to theexciting coil 1, causing the exciting coil 1 to build up promptly asshown by a curve 15a of FIG. 2. In this case, a joule loss occurring dueto a resistance of the exciting coil 1 will be compensated by the DCelectric power source at a last stage of the building-up period of theexciting current.

When the exciting current reaches the curve 14a, which changescorrespondingly with the standard voltage 14, the transistors 3a and 3bare turned off, and this causes the magnetic energy stored in theexciting coil 1 to be supplied to the capacitor 5 to decrease theexciting current steeply as shown by a curve 15b.

By repeating above cycle, the exciting current changes against its upperlimit of the curve 14a, as shown by ripple curves 15a˜15d in FIG. 2. Ascan be guessed from the fact that the exciting coil 1 and the capacitor5 have an electric characteristic similar to a parallel resonancecircuit in such a manner that a resonance frequency of the exciting coil1 and the capacitor 5 increases as the capacitance of the capacitor 5becomes small, a time width of respective exciting current sections15a˜15d is determined based on the capacitance of the capacitor 5, andthus it becomes small as the capacitance becomes small.

In the case of with a conventional apparatus which applies a high DCvoltage from the electric power source in order to facilitate thestorage and discharge of magnetic energy, there was a limitation inreducing the time width of respective exciting current sections 15a˜15d.That is, there was a limitation in increasing a chopper frequency.Accordingly, when the time width (shown by an arrow 8 in FIG. 2) of thestandard voltage 14 is decreased down to approximately 100 μsec, theresponsibility of exciting current to the standard voltage change willbe deteriorated substantially.

On the contrary, according to this embodiment, a good responsibility canbe maintained even in a high chopper frequency by using a smallcapacitance capacitor 5. Furthermore, it is not required to speciallyuse a high voltage and, therefore, a usual voltage corresponding to anexciting current flowing in the exciting coil 1 is sufficient for thecurrent supply control of this embodiment.

According to a measurement carried out by the inventors of thisapplication, in the case where an exciting coil of a reluctance typemotor having an output of approximately 300 watts is controlled by acurrent supply control apparatus using the capacitor 5 of 0.1 μF whichis similar to one defined in this embodiment, the exciting current 15sharply responded to the change of standard voltage 14 even in a highchopper frequency corresponding to an exciting current section width of0.5 μsec.

In this fashion, in accordance with the current supply control apparatusof this embodiment, the responsibility of exciting current to thestandard voltage can be improved in a large inductance load.

Accordingly, the magnetic levitation of the rotor member in the magneticbearing can be accomplished more accurately by executing the currentsupply control for the electromagnetic coil in the magnetic bearing asdescribed above.

Above-described first embodiment can be variously modified.

For example, instead of the current supply control for the exciting coilin the magnetic bearing, the current supply control apparatus of thefirst embodiment can be applied to a current supply control for anarmature (an exciting coil) of the motor.

Furthermore, the transistors 3a and 3b can be replaced by a high-speedswitching element such as an IGBT etc., whereby the responsibility inthe current supply control can be improved further.

Moreover, the standard voltage 14 shown in FIG. 2 can be replaced by asine-wave standard voltage in order to make this embodiment apparatusapplicable to an inverter-controlled device, whereby an inductionmachine capable of rotating at a high speed and being less subject tovibration can be obtained.

Though the back-flow preventing diode 6 is provided at the positiveoutput terminal 2a side of the DC electric power source in the firstembodiment, a diode 6a may be disposed at the negative output terminal2b side of the DC electric power source as shown by a broken line inFIG. 1. In this case, however, a capacitor 5b is connected in parallelwith the diode 6a.

FIG. 3 shows another modification of the first embodiment. This modifiedembodiment is different from the first embodiment in that the choppercircuit is constituted differently. That is, a differential circuit 11a,a monostable circuit 13 and an inversion circuit 13a are employedinstead of the amplification circuit 7 of FIG. 1.

When the exciting current exceeds the standard voltage 14 to change theoutput of the operational amplifier 11 from an L-level to an H-level,the differential circuit 11a generates a differential pulse. In responseto this differential pulse, the monostable circuit 13 is activated tooutput a pulse having a predetermined time width.

The width of output pulse is determined in accordance with a capacitanceof the capacitor 5. For example, it can be set to be equal to the timewidth of respective exciting current sections 15a˜15d shown in FIG. 2.This output pulse is supplied through the inversion circuit 13a to thetransistors 3a and 3b so as to turn off them.

Then, when the output pulse is extinguished, the transistors 3a and 3bwill be turned on again. That is, the chopper function is executed inthe same manner as the first embodiment. Also, as shown by a broken linein FIG. 3, the diode 6a may be interposed at the negative outputterminal 2b side of the DC electric power source, and the capacitor 5bmay be connected in parallel with the diode 6a.

Hereinafter, referring to FIGS. 4 and 5, a current supply controlapparatus in accordance with a second embodiment of the presentinvention applied to a two-phase reluctance type motor will beexplained.

The second embodiment apparatus serves as a current supply control unitfor controlling current supplied to a first-phase and a second-phasearmature coils (exciting coils) 1 and 1a in a two-phase reluctance typemotor, as a first and a second inductance loads, in response to positiondetecting signals 17a˜17d, - - - , shown in FIG. 5.

A circuit constitution relating to respective exciting coils 1 and 1a inthe current supply control apparatus is the same as the firstembodiment. In FIG. 4, circuit components relating to the first-phaseexciting coil 1 are suffixed by the same reference numeral ascorresponding components of FIG. 1, whereas circuit components relatingto the second phase exciting coil 1a are additionally suffixed byreference symbol a. Furthermore, two transistors relating to thesecond-phase exciting coil 1 are suffixed by the same reference numerals3c and 3d, whereas two diodes are suffixed by reference numerals 4c and4d.

A first standard voltage input terminal 12 is applied withrectangular-waveform position detecting signals 17a, 17c, - - - . Whichare successively outputted at regular intervals of a predeterminedelectric angle from a position detecting device (not shown) inproportion to a rotational position of a rotor of the two-phasereluctance motor (not shown), whereas a second standard voltage inputterminal 12a is applied with rectangular-waveform position detectingsignals 17b, 17d, - - - . These position detecting signals17a˜17d, - - - have a width of the same electric angle.

In the current supply control apparatus constituted as above, when theposition detecting signal 17a of an H-level is inputted to the firststandard voltage input terminal 12, the chopper control is carried outin the same way as the first embodiment, and an exciting currentcorresponding to a value of the position detecting signal 17a flows inthe first-phase exciting coil 1. When the H-level signal 17a isextinguished, the transistors 3a and 3b are turned off, causing thecapacitor 5 to be charged by a current occurring due to the discharge ofthe magnetic energy stored in the first-phase exciting coil 1.

Subsequently, when the position detecting signal 12b is inputted to thesecond standard voltage input terminal 12a of the current supply controlapparatus, an output of the operational amplifier 11a becomes anH-level, since an output of the absolute value circuit 10a is not largerthan the magnitude of the signal 12a. Accordingly, the transistors 3cand 3d are turned on in response to an output from the amplificationcircuit 7a.

In this instance, both the charged voltage in the capacitor and thevoltage of the DC electric power source are applied to the second-phaseexciting coil 1a to cause the exciting current flowing in the excitingcoil 1a to build up sharply. After that, the electric power sourcevoltage is applied through the diode to the exciting coil 1a maintain acurrent supply to the exciting coil 1a.

Further, by virtue of the function performed by the chopper circuitincluding the operational amplifier 11a, the exciting current can bemaintained at a magnitude proportional to the position detecting signal17b. When the signal 17b is extinguished to deactivate the exciting coil1a, the magnetic energy stored in the exciting coil 1a is supplied tothe capacitor 5 through the diodes 4c and 4d to charge it up to a highvoltage. Thus, the magnetic energy is converted into the electrostaticenergy of the capacitor 5.

Moreover, due to this energy conversion, the exciting current flowing inthe exciting coil 1 decreases steeply. Next, in response to anapplication of the position detecting signal 17c to the input terminal12 of the current supply control apparatus, the exciting current flowingin the first exciting coil 1 builds up rapidly, is chopper-controlledand finally decreased steeply.

In FIG. 5, broken lines 18a˜18d denote exciting currents; an arrow 19adenotes a section of an electric angle of 180 degrees; and an arrow 19bdenotes a current supply section of, for example, 150 degrees.

As is described above, since both building-up and trailing-off of theexciting current are steep, torque reduction in the building-up periodof the exciting current and counter torque generation in itstrailing-edge period are fairly suppressed compared with a conventionalreluctance type motor, and this enables a reluctance type motor equippedwith an armature (an exciting coil) having a remarkably large inductanceto be driven at a higher speed.

An above-described second embodiment can be modified variously.

For example, the second embodiment can be modified for applicationapplied to a three-phase reluctance type motor having a first-, asecond-, and a third-phase armature coils 1, 1a and 1b as a first, asecond, and a third inductance load. In general, respective phasearmature coils 1, 1a and 1b are formed from a plurality of armaturecoils to be supplied with the same-phase exciting current. The currentsupply control apparatus of this modified embodiment relates to thethird-phase armature coil 1b and includes a circuit block A shown by abroken line in FIG. 4. The circuit block A includes the same circuitcomponents as those relating to the first- and second-phase armaturecoils 1 and 1a.

An input terminal 12 of the current supply control circuit relating tothe first-phase armature coil 1 is supplied with position detectingsignals 20a, 20b, - - - each having a width of a 180-degree electricangle and spaced 180 degrees from each other (as shown in FIG. 5). Inresponse to these position detecting signals, a current supply controlof the first-phase armature coil 1 is carried out in the same manner asthe second embodiment.

Similarly, in response to the position detecting signals 21a, 21b, - - -supplied to the input terminal 12a, a current supply control of thesecond-phase armature coil 1a is carried out, whereas, in response tothe position detecting signals 22a, 22b, - - - supplied to the inputterminal 12b, a current supply control of the third-phase armature coil1b is carried out. Phases of the position detecting signals 21a,21b, - - - are delayed by a 120-degree electric angle from those of theposition detecting signals 20a, 20b, - - - respectively, whereas phasesof the position detecting signals 22a, 22b, - - - are delayed by a120-degree electric angle than those of the position detecting signals21a, 21b, - - -respectively.

Accordingly, a phase of the exciting current flowing through thesecond-phase armature coil 1a is delayed by an electric angle of 120degrees from a phase of the exciting current flowing through thefirst-phase armature coil 1, whereas a phase of the exciting currentflowing through the third-phase armature coil 1b is delayed by anelectric angle of 120 degrees from the phase of the exciting currentflowing through the second-phase armature coil 1a . According to thismodified embodiment, respective phase exciting current having asubstantially rectangular waveform can be obtained. Thus, the motor canbe driven at a high-speed.

The second embodiment can be modified for application to an n-phase DCmotor including n-pieces (n=2, 3, - - - ) of armature coil as inductanceloads. The n-pieces of the armature coil are respectively formed of aplurality of armatures being supplied with the same-phase current.

The current supply control apparatus of the above modified embodiment issupplied with position detecting signals of different phases beingsuccessively delayed by (360/n) degrees. Position detecting signals ofdifferent phases have the same 180-degree width and spaced 180 degreesfrom each other. The current supply control apparatus includes n piecesof back-flow preventing diode and n pieces of small capacitancecapacitor, which are respectively corresponding to n pieces ofinductance load. And, in response to application of respective phaseposition detecting signals, respective phase armature coils aresuccessively supplied exciting current of electric angle width of 180degrees with a (360/n)-degree phase difference.

Moreover, the second embodiment can be modified for application to ann-phase stepping motor. In this case, the same current supply controlapparatus as the one applied to the above modification for the n-phaseDC motor is used. The current supply control apparatus executes thecurrent supply control on the basis of position detecting signals ofdifferent phases differing by a time width of 2T/n (T denotes apredetermined time width) from each other.

Hereinafter, with reference to FIG. 6, a current supply controlapparatus in accordance with a third embodiment of the presentinvention, which is applied to a motor, will be explained.

This embodiment has basically the same constitution as the firstembodiment (FIG. 1). The common circuit components are suffixed by thesame reference numerals, and so their explanations are partly omittedhere. This embodiment basically functions in the same way as the firstembodiment. Thus, the explanation of its operation is partly omitted.FIG. 6 shows circuit components relating only to one phase of the motor.

The current supply control apparatus shown in FIG. 6 comprises an ANDcircuit 48a having one input terminal being connected to the outputterminal of the operational amplifier 11 instead of the amplificationcircuit 7 of FIG. 1. The AND circuit 48a has the other input terminal47a to which a position detecting signal (not shown) representing therotational position of the motor's rotor is supplied.

The standard voltage input terminal 12 is supplied with an excitingcurrent control voltage (not shown) corresponding to the standardvoltage 14 of the first embodiment. Further, the capacitor 5 isconnected in series to the back-flow preventing diode 6.

Moreover, the current supply control apparatus includes an inductance41a constituted by a ferrite magnetic core having a closed magnetic pathand associated with a coil. This charging inductance 41a has its one endconnected to an operational voltage terminal 2c provided, for example,for the divided voltage of the DC electric power source, whereas itsother end being not only connected through the transistor 43c and aresistance to the negative output terminal 2b of the DC electric powersource but also connected through the diode 44c to the capacitor 5.

A base of the transistor 43 is connected through a resistance to acontrol voltage input terminal 47, and also connected through thetransistor 43d to an output terminal of an AND circuit 48a.

With above arrangement, if an H-level position detecting signal isapplied to the AND circuit 48a in the condition where the excitingcurrent control voltage 14 is applied to the standard voltage inputterminal 12 and the gate of AND circuit 48a is opened in response to anH-level signal fed from the operational amplifier 11, the transistors 3aand 3b will be activated.

On the other hand, when the position detecting signal is extinguished,the transistors 3a and 3b are turned off. In response to the turning onand off of the transistors 3a and 3b, each component of the currentsupply control apparatus functions in the same fashion as the firstembodiment to control the exciting coil 1. Thus, the exciting currentflowing through the exciting coil 1 builds up rapidly and then ismaintained at a value corresponding to the exciting current controlvoltage to decrease rapidly in the end.

During above current supply control operation, not only joule lossoccurs due to a resistance of the exciting coil 1 but iron loss occursin a magnetic core of the exciting coil 1. These energy losses tend toincrease as the inductance of the exciting coil 1 increases and also asthe chopper frequency increases, thereby sometimes ending up with a lossof approximately 30%.

If the energy loss increases, an electrostatic energy stored in thecapacitor 5 decreases. Furthermore, a conversion loss increases when theelectrostatic energy is converted into the magnetic energy. In thiscase, the exciting current 15 does not respond quickly to the excitingcurrent control voltage 14 applied to the standard voltage inputterminal 12. This embodiment can solve such a disadvantage by utilizingfunction of the charging inductance 41a.

More particularly, when the control voltage input terminal 47 is appliedwith a positive voltage to turn on the transistor 43c, the charginginductance 41a is applied with an operational voltage from theoperational voltage terminal 2c. Thus, a magnetic energy is stored inthe charging inductance 41a. In such a condition, if an H-level outputis sent out from the AND circuit 48a, the exciting coil 1 is suppliedwith exciting current and the transistor 43d is turned on, therebycausing simultaneous deactivation of the transistor 43c.

In this instance, as is explained with reference to FIG. 1, the excitingcoil 1 is not only applied with the voltage of the DC electric powersource but also applied with the voltage charged in the capacitor 5 byvirtue of the magnetic energy stored in the exciting coil 1.

In addition to this, in this embodiment, the magnetic energy stored inthe inductance 41a is supplied through the diode 4c to the capacitor 5in an initial stage of the current supply period to have the capacitor 5charged with polarities shown in the drawing. As a result, the magneticenergy is converted into the electrostatic energy. Accordingly, a chargevoltage of the capacitor 5, which has already been charged with themagnetic energy stored in the exciting coil 1, will further beincreased. Consequently, the exciting current flowing through theexciting coil 1 will be increased sharply.

Next, when an output of the AND circuit 48a is changed from an H-levelto an L-level, the exciting coil 1 is deactivated to cause the capacitor5 to be charged with the magnetic energy stored in the exciting coil 1.At the same time, the transistor 43d is turned off, whereas thetransistor 43c is turned on to let current flow in the inductance 41a tostore a magnetic energy therein.

As is understood from the above explanation, energy lost in the form ofcopper loss and iron loss is compensated from the charging inductance41a through the diode 44c. Accordingly, both the building-up andtrailing-off of exciting current become steep. That is, theresponsibility in the current supply control can be improved.

Further, it is desirable for the charging inductance 41a to be suppliedwith a current having a magnitude determined based on the excitingcurrent value. For this reason, an operational voltage proportional tothe voltage applied to the standard voltage input terminal 12 is appliedthrough the terminal 2c to the charging inductance 41a. Otherwise, avoltage proportional to the exciting current control voltage 14 isapplied from the terminal 47 to the base of the transistor 43c thatoperates in an active region.

This third embodiment can be variously modified.

For example, though the capacitor 5 in the third embodiment is chargedwith the magnetic energy stored in the charging inductance 41a at thetiming the exciting current flowing the exciting coil 1 builds up, it isalso preferable to charge the capacitor 5 at the time point at which theexciting current trails off. In this case, as shown by a broken line inFIG. 6, an inversion circuit 43e is inserted.

Furthermore, the third embodiment can be modified as shown in FIG. 7.This modified embodiment corresponds to the modified embodiment of thefirst embodiment (FIG. 3), and basically operates in the same manner asthe third embodiment and the modified embodiment of the first embodiment(FIG. 3).

When the charging inductance 41a is deactivated, the capacitor 5 ischarged with the discharge of magnetic energy stored in the inductance41a to have polarities shown in the drawing, and a voltage equal to asum of the DC electric power source voltage and the capacitor chargedvoltage is applied to the exciting coil 1 to sharply build up theexciting current. Subsequently, the exciting current decreases steeply.

Furthermore, the third embodiment can be modified in the same manner asother modifications explained in conjunction with the first embodiment.

Hereinafter, referring now to FIG. 8, a current supply control apparatusin accordance with a fourth embodiment of the present invention appliedto a three-phase full-wave reluctance type motor will be explained.

In FIG. 8, a reference numeral 1 denotes a first-phase exciting coil fora motor, whereas a reference numeral 1--1 denotes a second-phaseexciting coil. The third-phase exciting coil is omitted here. Thecircuit components corresponding to the first-phase exciting coil 1 areexplained in detail, whereas the circuit components corresponding to thesecond-phase exciting coil 1--1 are simplified by showing them as ablock A' in the drawing, and the circuit components relating to thethird-phase exciting coil is omitted.

The current control apparatus is constituted in such a manner that thefirst-, the second-, and the third-phase exciting coils provided asinductance loads are successively activated in a half-wave currentsupply mode in response to rectangular-waveform position detectingsignals supplied to three input terminals (two of them are suffixed byreference numerals 47a, 47b). The position detecting signals supplied tothe input terminal 47a are suffixed by reference numerals 117a, 117b,and the position detecting signal supplied to the input terminal 47b issuffixed by a reference numeral 118a in FIG. 9.

These position detecting signals 117a, 117b, - - - have the same widthof a 120-degree electric angle and also have a 360-degree phasedifference with each other. The position detecting signals 118a, - - -have a 180-degree phase difference with respect to the positiondetecting signals 117a, 117b, - - - .

In a conventional reluctance type motor, when the current supply to theexciting coil 1 is initiated in response to an application of theposition detecting signal 117a, the exciting current builds up slowlyalong a curve 119 shown in FIG. 9 because of a large inductance of theexciting coil 1, thereby causing the motor output torque to decreases.

Furthermore, when the current supply is stopped, the exciting currentdecreases slowly because of the magnetic energy stored in the excitingcoil 1. Accordingly, the exciting current flows even at outside of thepositive torque generating section 121a of 180 degrees, thereby causinga counter torque to occur.

When the motor is driven at a high speed, a width of the positiondetecting signal 117a decreases, whereas a width of torque reductiongenerating section or a width of counter torque generating section willnot decrease, and thus the current supply section width decreases as awhole, thereby making a high-speed driving operation difficult.

In order to solve above problem, this embodiment is constituted in thesame manner as the third embodiment. That is, at the time point at whichthe current supply to respective exciting coil is stopped or started,the capacitor 5 is charged or discharged to sharply build up theexciting current or to steeply decrease it. With this arrangement, thecurrent supply to exciting coil of each phase can be carried out duringthe position detecting signal width.

Furthermore, the charging inductance 41a is activated during a widthcorresponding to the position detecting signal to store the magneticenergy. Therefore, the copper loss and the iron loss occurring in theexciting coil at the time point at which the current supply to theexciting coil is stopped or started are compensated by the magneticenergy stored in the charging inductance 41a. Thus, both the building-upand the trailing-off of the exciting current become so sharp that themotor can be driven at a high speed of 100,000 rpm with a large outputtorque.

Hereinafter, an operation of the current supply control apparatus ofFIG. 8 will be explained.

An AND circuit 48a, transistors 3a, 3b, diodes 4a, 4b, a resistance 9,and an absolute value circuit 10 respectively function in the samemanner as the third embodiment shown in FIG. 6. A positive inputterminal of the operational amplifier 11 is applied with a voltageobtained by dividing the standard voltage 14 (FIG. 2) of the standardvoltage input terminal 12 by the resistance 9'. Consequently, theexciting current flowing through the first-phase exciting coil 1 ischopper-controlled to a value corresponding to the standard voltage 14as shown by a curve 122b in FIG. 9.

Moreover, the operational amplifier 11' and its peripheral circuitcomponents function in the same manner as the corresponding circuitcomponents of the third embodiment. One input terminal of the ANDcircuit 48b is supplied with a position detecting signal 117a (FIG. 9)of an H-level, which is to be inputted to the AND circuit 48a.Therefore, during a period of the position detecting signal 117a, thecharging inductance 41a is supplied with a current having a valuerestricted by the standard voltage 14. During this period, a dischargedcurrent of the capacitor 5 is supplied through the diodes 44c and 44d tothe charging inductance 41a when the transistor 43c is turned off bybeing chopper-controlled.

When the position detecting signal 117a is changed from an H-level to anL-level, the transistors 3a and 3b are turned off. In this instance, adischarging current derived from the magnetic energy stored in theexciting coil 1 charges the capacitor 5 to polarities shown in thedrawing through the diodes 4a, 4b, and the DC electric power sources 2aand 2b.

At the same time, the capacitor 5 is charged with the magnetic energystored in the charging inductance 41 a through the diodes 44c and 44d.Accordingly, the capacitor 5 can be charged up to a high voltage.

Furthermore, in response to the application of H-level positiondetecting signals 118a, - - - to the input terminal 47b of the currentsupply control apparatus, transistors connected to both ends of thesecond-phase exciting coil 1--1 are turned on to initiate the excitingcurrent supply. In this case, a voltage corresponding to a sum of thecharged voltage of capacitor and the voltage of DC electric power sourceis applied to the exciting coil 1--1, and the exciting current builds upsharply as shown by a curve 123 of FIG. 9.

Subsequently, by virtue of a chopper function of the operationalamplifier 11 etc., the exciting current is chopper-controlled as shownby a broken line 123a. Then, when the position detecting signal 118aturns from an H-level to an L-level, both the transistor connected tothe exciting coil and the transistor 43c connected to the charginginductance 41a are turned off simultaneously to cause exciting currentto decrease steeply as shown by a curve 123c.

In FIG. 9, the curve 122d shows the exciting current flowing in thefirst-phase exciting coil 1 in response to the position detecting signal117b supplied to the input terminal 47a.

As shown in FIG. 9, since each width of the exciting current curve122a˜122c is in a section 121b of a 180-degree electric angle, nocounter torque is generated.

Furthermore, since the exciting current has substantially arectangular-waveform, no torque reduction is generated.

Further, in order to make the building-up and the trailing-off of theexciting current steep, the capacitance of the capacitor 5 is dependingon the value of a current flowing in the exciting coil and an inductancevalue of the exciting coil. Further, an inductance value of the charginginductance 41a and the value of a current flowing in the charginginductance 41a are determined based on the same criterion.

Still further, it is possible to drive the motor at a constant speed byvarying the standard voltage 14 to rotational speed of the motor.

FIG. 10 shows a modified embodiment of the current supply controlapparatus of the fourth embodiment (FIG. 8).

This modified embodiment differs from the fourth embodiment in that anoutput of the operational amplifier 11 is fed to only one (for example,the transistor 3a) of two transistors connected to both ends of eachphase exciting coil, and also in that the capacitor 5 is connected inparallel with a back-flow preventing diode 6 interposed between theexciting coil and the DC electric power source.

In the modified embodiment of FIG. 10, when the position detectingsignal 117a is supplied to the input terminal 47a, the transistors 3aand 3b are turned on to activate the first-phase exciting coil 1. On theother hand, if the exciting current increases and the voltage appliedbetween both ends of the resistance 9 exceeds the standard voltage 14 ofthe positive input terminal of the operational amplifier 11, a gate ofthe AND circuit 8a is closed to turn off the transistor 3a.

With this arrangement, the magnetic energy stored in the exciting coil 1is discharged through the transistor 3b, the resistance 9 and the diode4b, and the exciting current is decreased. When the exciting currentdecreases down to a set value, an output of the operational amplifier 11returns to a H-level due to a hysteresis characteristic of theoperational amplifier 11, whereby the transistor 3a is turned on againto increase the exciting current.

Owing to such a chopper function, the exciting current can be maintainedat a set value. When the position detecting signal 117a is extinguished,the transistors 3a and 3b are turned off together.

The magnetic energy stored in the exciting coil 1 charges the capacitor5 to polarities shown in the drawing though the diodes 4a and 4b. Thus,the magnetic energy decreases rapidly, and the exciting current trailsoff steeply.

Since a gate of the AND circuit 48b is opened or closed in response tothe position detecting signal 117a, the control of the current supply tothe charging inductance 41a is carried out corresponding to a durationof the position detecting signal 117a.

And, under the control of chopper circuit consisting of the AND circuit48b, the resistance 49b, the operational amplifier 11' etc., thecharging inductance 41a is supplied with a current corresponding to thestandard voltage 14.

Then, if the position detecting signal 117a is extinguished to turn offthe transistor 43c, the magnetic energy stored in the charginginductance 41a charges the capacitor 5 up to a high voltage through thediode 44c. Accordingly, the exciting current flowing in the excitingcoil 1 decreases steeply.

Similar current supply control is carried out with respect to thesecond-phase and third-phase exciting coils.

The fourth embodiment can be further modified variously. For example,instead of the capacitor 5, a capacitor 5a can be provided as shown by abroken line in FIG. 10. Moreover, the fourth embodiment can be modifiedso as to be applied to a three-phase brushless motor having a magnetrotor. In this case, since the armature coil has a small inductance, themotor can be driven at a further high-speed.

Hereinafter, with reference to FIG. 11, a current supply controlapparatus in accordance with a fifth embodiment of the present inventionapplied to a six-phase half-wave stepping motor will be explained.

A conventional large-size, high-output torque, stepping motor a largeinductance armature coil and a long stepping time, and thus it was notpossible for such a motor to promptly move the load connected to themotor. Especially, this kind of problem is conspicuous in a reluctancetype stepping motor, though it can provide a large output torque. Thisembodiment aims to solve such a problem.

In FIG. 11, a current supply control circuit component relating to thefirst-phase armature coil (inductance load) 1 and the charginginductance 41a is illustrated in detail, and current supply controlcircuit components relating to the second- to sixth-phase armature coils1-1˜1-5 and the charging inductances 41b˜41f aare briefly illustrated bymerely showing blocks B˜F.

Input terminals 47a˜47f of the first- to sixth-phase circuit componentsapplied with first- to sixth-phase rectangular-waveform pulse signals124a, 124b, - - - , 125a, 125b, - - - , 126a, 126b, - - - 127a,127b, - - - 128a, 128b, - - - 129a, 129b, - - - (FIG. 12). The pulsesbelonging to the same phase have a mutual phase difference of a180-degree electric angle, and, respective phase pulses are spaced by 60degrees from each other.

When the pulse signal 124a is inputted to the input terminal 47a, anexciting current 124a' flows in the first armature coil 1. In the samemanner as above-described various embodiments, the exciting currentbuilds up sharply. Then, when a next pulse signal 124b is supplied tothe input terminal 47a, a high voltage corresponding to a sum of thecharged voltage in the capacitor 5 and the voltage of the DC electricpower source is applied to the armature coil 1, causing the excitingcurrent 124b' to builds up sharply.

When the pulse signal 124b is extinguished to deactivate the armaturecoil 1, the magnetic energies stored in the armature coil 1 and thecharging inductance 41a are converted into the electrostatic energy inthe capacitor 5 to charge the capacitor 5 with a high voltage. Thus, theexciting current 124b' decreases rapidly. In this manner, regardless ofthe value of inductance load, the current supply to the first-phasearmature coil can be executed during a time width corresponding to apulse signal width even if the motor rotational speed is increased.

In the same way, the current supply to the second- to sixth-phasearmature coils can be executed during time widths corresponding torespective pulse signal widths. Thus, the stepping operations in themotor can be executed at a high speed.

What is claimed is:
 1. A current supply control apparatus for aninductance load comprising:first and second switching elementsinterposed between a DC electric power source and the inductance load;first and second diodes inversely connected to respective ones of saidfirst and second switching elements and the inductance load; currentdetecting means for generating a detecting voltage representing acurrent flowing in the inductance load; a back-flow preventing diodeconnected in a forward direction with respect to the DC electric powersource on the DC electric power source side; a capacitor connected tosaid back-flow preventing diode; and a chopper circuit for comparingsaid detecting voltage from said current detecting means with a standardvoltage variably set in a voltage waveform for turning on or off saidfirst and second switching elements depending on the result of thecomparison, said chopper circuit including:an absolute value circuit,connected to said current detecting means, for detecting a voltage dropin said current detecting means; when the detecting voltage exceeds thestandard voltage, said first and second switching elements are turnedoff, during the turning-off period of said switching elements, amagnetic energy stored in the inductance load is prevented from beingreturned to the DC electric power source by said back-flow preventingdiode, the magnetic energy is supplied to said capacitor through saidfirst and second diodes to charge said capacitor, thereby causing acurrent flowing in the inductance load to be quickly reduced after saidswitching elements have been turned off, and when the detecting voltagedecreases to a predetermined value, said first and second switchingelements are turned on to cause a high voltage equal to a sum of avoltage charged in said capacitor and a voltage of the DC electric powersource to be applied to the inductance load so that a current flowing inthe inductance load can be increased sharply.
 2. A current supplycontrol apparatus in accordance with claim 1, further comprising:acharging inductance; a third switching element interposed between saidback-flow preventing diode and said charging inductance; and a thirddiode interposed between said charging inductance and said capacitor,wherein, a magnetic energy stored in said charging inductance issupplied to said capacitor through said third diode when said thirdswitching element is turned off.
 3. A current supply control apparatusfor n-sets of inductance loads, comprising:n sets of semiconductorswitching elements respectively connected to both ends of the n sets ofinductance loads, n being a positive integer; a DC electric power sourcefor supplying exciting current to the n sets of inductance loads throughsaid n sets of semiconductor switching elements; inversely connecteddiodes inversely connected to connecting units each including respectiveones of said n sets of semiconductor switching elements and respectiven-sets of inductance loads; a current detecting circuit for detecting anexciting current flowing in said n sets of inductance loads to obtain nsets of detecting voltage; back-flow preventing diodes respectivelyconnected in a forward direction with respect to said DC electric powersource on a DC electric power source side; n capacitors having a smallcapacitance and connected in parallel with said back-flow preventingdiodes; n sets of rectangular-waveform signal rows having apredetermined width and a predetermined phase difference; and circuitmeans including a chopper circuit including an absolute value circuitconnected to said current detecting circuit for detecting a voltage dropin said current detection circuit, said circuit means being formed suchthat said n sets of semiconductor switching elements are turned on toactivate the n sets of inductance loads in response to said n sets ofrectangular-waveform signal rows, and a corresponding one of said n setsof semiconductor switching elements is turned off when each of said nsets of detecting voltage exceeds a set value, a magnetic energy storedin the n sets of inductance loads is prevented from being returned tosaid DC electric power source by an action of said back-flow preventingdiode, and the magnetic energy is converted into electrostatic energy ofsaid n capacitors through said inversely connected diodes so that acurrent flowing in said inductance load is quickly reduced and when thedetecting voltage has decreased to a predetermined value, saidcorresponding one of said semiconductor switching elements is turned onto cause a high voltage equal to a sum of a voltage charged in said ncapacitors and a voltage of said DC electric power source to be appliedto the n sets of inductance loads so that current flowing in the n setsof inductance loads can be increased sharply.
 4. A current supplycontrol apparatus for inductance loads comprising:first and secondinductance loads; first and second sets of semiconductor switchingelements respectively connected to both ends of said first and secondinductance loads; a DC electric power source for supplying excitingcurrent to said first and second inductance loads through said first andsecond sets of semiconductor switching elements; inversely connecteddiodes, inversely connected to respective serial connecting unitsincluding respective semiconductor switching elements and respectiveinductance loads; a first current detecting circuit for detectingexciting current flowing in said first and second inductance loads toobtain a first detecting voltage; back-flow preventing diodesrespectively connected in a forward direction with respect to said DCelectric power source on a DC electric power source side; capacitorsconnected in parallel with said back-flow preventing diodes; a third setof semiconductor switching elements; a charging inductance supplied withcurrent through said third set of semiconductor switching elements fromsaid DC electric power source; a second current detecting circuit fordetecting exciting current flowing in said charging inductance to obtaina second detecting voltage; a current supply control circuit, connectedto said first, second and third sets of semiconductor switchingelements, responding to odd signals included in a row ofrectangular-waveform signals each having a predetermined time width andbeing spaced from each other with a predetermined phase difference toturn on said first set of semiconductor switching elements during saidpredetermined time width to activate said first inductance load,responding to even signals included in said row of rectangular-waveformsignals to turn on said second set of semiconductor switching elementsduring said predetermined time width to activate said second inductanceload, and further responding to all signals included in said row ofrectangular-waveform signals to turn on said third set of semiconductorswitching elements during said predetermined time width to activate saidinductance loads; an electric circuit for discharging magnetic energystored in said charging inductance to charge said capacitors throughsaid inversely connected diodes to a joint point of said charginginductance and said third semiconductor switching element, when saidthird semiconductor switching element is turned off; a first choppercircuit for comparing the first detecting voltage with a standardvoltage commanding an exciting current flowing in said first and secondinductance loads, as well as for controlling the on and off of saidfirst and second sets of semiconductor switching elements depending onthe result of such comparison so that the exciting current flowing insaid first and second inductance loads can be maintained at a valuecorresponding to said standard voltage; and a second chopper circuit forcomparing the second detecting voltage with said standard voltage, andcontrolling the on and off of said third set of semiconductor switchingelements depending on the result of the comparison so that the excitingcurrent flowing in said charging inductance can be maintained at a valuecorresponding to said standard voltage, said electric circuit beingformed such that, when one of said first and second inductance loads isdeactivated in response to extinction of respective signals of said rowof rectangular-waveform signals, magnetic energy stored in said one ofsaid first and second inductance loads and said charging inductancebeing prevented from returning to said DC electric power source by saidback-flow preventing diode, is converted through said inverselyconnected diodes into an electrostatic energy of said capacitor tocharge said capacitor with a high voltage, thereby quickly reducing theexciting current flowing in said inductance loads, when the currentsupply control to the other one of said first and second inductanceloads is initiated in response to an application of a next signal ofsaid row of rectangular waveform signals, the exciting current of saidother one of said first and second inductance loads is sharply increasedby the charged voltage of said capacitors.
 5. A current supply controlapparatus for inductance loads comprising:a plurality of inductanceloads; plural sets of semiconductor switching elements respectivelyconnected to both ends of said plurality of inductance loads; a DCelectric power source for supplying exciting current to said pluralityof inductance loads through said plural sets of semiconductor switchingelements; inversely connected diodes inversely connected to respectiveserial connecting units including respective ones of said plural sets ofsemiconductor switching elements and respective inductance loads; afirst current detecting circuit for detecting exciting current flowingin said plurality of inductance loads to obtain a first group ofdetecting voltages; a plurality of back-flow preventing diodesrespectively connected in a forward direction with respect to said DCelectric power source on a DC electric power source side; a plurality ofcapacitors connected in parallel with said plurality of back-flowpreventing diodes; a plurality of charging inductances supplied withcurrent from said DC electric power source through said plural sets ofsemiconductor switching elements; a plurality of diodes inverselyconnected to respective joint points of said plurality of charginginductances; a second current detecting circuit for detecting excitingcurrent flowing in said plurality of charging inductances to obtain asecond group of detecting voltages; a first chopper circuit forresponding to said second group of detecting voltages to supply acurrent proportional to a standard voltage commanding an excitingcurrent of said plurality of inductance loads to a corresponding one ofsaid plurality of charging inductances; a first current supply controlcircuit, responding to a plurality of signal rows consisting of pluralsignals each having a predetermined time width and being generated atpredetermined intervals, said signal rows being spaced from each otherwith a predetermined phase difference, and turning on said plural setsof semiconductor switching elements during said predetermined time widthto activate said plurality of inductance loads; a second current supplycontrol circuit, responding to said plurality of signal rows to turn onsaid plural sets of semiconductor switching elements only during saidpredetermined time width to activate said plurality of charginginductances; an electric circuit for discharging a magnetic energystored in said plurality of charging inductances to charge acorresponding one of said plurality of capacitors through a respectiveone of said plurality of diodes and a corresponding one of said pluralsets of semiconductor switching elements, when respective ones of saidplural semiconductor switching elements are turned off; and a secondchopper circuit for comparing the first group of detecting voltages withsaid standard voltage to control said plural sets of semiconductorswitching elements to be ON and OFF depending on the result of thecomparison so that the exciting current flowing in said plurality ofinductance loads can be maintained at a value corresponding to saidstandard voltage, said electric circuit formed such that, when one ofsaid plurality of inductance loads is deactivated in response toextinctions of respective signals of said signal rows, magnetic energystored in one of said plurality of inductance loads and a correspondingcharging inductance are prevented from returning to said DC electricpower source by the action of a corresponding one of said plurality ofback-flow preventing diodes, is converted through a respective one ofsaid inversely connected diodes into electrostatic energy of acorresponding one of said plurality of capacitors to charge saidcorresponding one of said plurality of capacitors with a high voltageand to quickly reduce the exciting current flowing in said one of saidplurality of inductance loads, and when the current supply control toanother one of said plurality of inductance loads is initiated inresponse to an application of a next signal of said plurality of signalrows, the exciting current of said another one of said plurality ofinductance loads is sharply increased by the charged voltage of saidcorresponding one of said plurality of capacitors.